Push-pull amplifiers are generally known, e.g., as disclosed in U.S. Pat. No. 2,201,345 A.
U.S. Pat. No. 1,964,048 A and the corresponding German Patent Specification 592 184 disclose, for the purpose of common-mode rejection, connecting a coil arrangement into a line pair, said coil arrangement consisting of two coils that are wound in the same sense and are wound in one another and thus closely coupled to one another.
In order to amplify an input signal to be amplified, it is known to use a half-bridge circuit in which the two active components (transistors, tubes) are connected in series. In this configuration, the so-called “high-side component” has to have a high AC and DC voltage potential with respect to ground. In this configuration, parasitic capacitances for example from the component housing with respect to ground in practice introduce an unbalance into the circuit. Furthermore, the balanced driving of the active components turns out to be difficult owing to the greatly different stray capacitances. Other embodiments having balanced ground reference of the components require a power balancing and combination element, for example a transformer, at the output.
Push-pull amplifiers are also known in which the active and passive components are arranged symmetrically. Thus, by way of example, corresponding circuits are known by the designations customary to those skilled in the art: “parallel push-pull”, “circlotron” and push-pull half-bridge circuit, which balance the potentials of the active components in the desired manner.
However, two separate voltage supplies are required for these circuits. Furthermore, the driving is superposed in principle with respectively half of the output voltage, such that the theoretically maximum voltage gain is limited to a factor of 2 and even this value is often not achieved in practice. In the kilohertz frequency range, a so-called “bootstrap circuit” of the driver stage is used in order to reduce this extremely high negative feedback. At higher frequencies, however, this circuit cannot be used owing to the strong interference influence of stray capacitances.
U.S. Pat. No. 2,201,345 cited in the introduction discloses a symmetrically constructed push-pull amplifier in which a common voltage supply is present. However, in this push-pull amplifier, too, the achievable gain is limited to the value of two.